1. Field of the Invention
This invention relates to rolls as used in systems to extrusion form products and, more particularly, to a roll that can be selectively skewed relative to a cooperating roll.
2. Background Art
In conventional extrusion forming systems, moldable material is deposited at a nip location between cooperating rolls that are supported at their axial ends upon a frame. By turning the rolls around parallel axes, material is formed to a thickness determined by the gap between the rolls. A problem that is commonly encountered with these systems is the deformation of typically a smaller diameter roll in a cooperating roll pair caused by the thickness of the extruded material during product formation. The material tends to produce a wedging action that causes the unsupported central region of the smaller diameter roll in the cooperating roll pair to deform to a shallow arch shape. It is difficult to maintain a uniform product thickness when this condition occurs. If no accommodation is made for this roll deformation, the quality of the formed product may be compromised.
Further, the arching of the roll tends to produce significant forces upon the ends of a shaft that support the roll upon the frame. In anticipation of this occurring, the shaft and supporting structure may be made with a more robust, and potentially more expensive, construction.
It is also known to skew the deformed roll to place its axis at a slight angle to the axis of the cooperating roll. This causes the arch shape to more closely conform to the cooperating roll, as a result of which there is a more uniform gap dimension over the full axial extent of the rolls, even with the deformation of the one roll maintained.
Heretofore, skew mechanisms have been designed so that the shaft ends on the skewed roll are offset in a manner whereby the supports for the shaft ends on the frame are subjected to potentially large forces. In essence, the parts become misaligned so that as the system is operated, the interacting parts, such as the shaft ends, bearings, and supports, are prone to becoming worn, and may ultimately be prone to failing.
A failure of a part or parts on cooperating components on an extrusion forming line may necessitate shutting the entire line down. This down time can have significant economic consequences, particularly in operations where profit margins are thin.
This industry continues to develop overall system designs that are economically feasible, yet highly reliable in operation, thereby to avoid, or minimize, system downtime. The same design criteria drive the design of skew mechanisms. In spite of designers' striving to meet the above objectives, existing, commercially available systems that allow roll skewing are deficient in one or more respects. The industry continues to seek out improved designs for skew mechanisms on extrusion forming systems.